Spray application of plastics additives to polymers

ABSTRACT

A process for applying a polymer additive material to a polymeric substrate includes the steps of a) forming in a closed pressurized system a mixture of a solid polymer additive material, a suitable liquid carrier material, and a suitable viscosity reducing material, and b) spraying this mixture onto a polymeric substrate.

FIELD OF THE INVENTION

This application relates to introduction of plastics additives intopolymeric materials, and more particularly, to a process for the sprayapplication of plastics additives to polymeric materials.

BACKGROUND

In the manufacture of products using thermoplastic resins such aspolyolefins, various additives are generally included in the resin toaffect color, to ease processability, and to inhibit oxidation and othertypes of degradation, to stabilize the physical characteristics of theresin and thus prolong the life expectancy of the product.

For maximum effectiveness, it is important that any additive beuniformly distributed in the thermoplastic resin. Poorly distributedadditives may contribute to unsatisfactory properties in the finalproduct, such as reduced tensile and tear strengths, reduced resistanceto low temperature flexing, reduced elongation characteristics, reducedbreakdown voltage strengths of dielectric materials, and electricallosses caused by an increased power factor and increased dielectricconstant.

The physical form of plastics additives can determine the efficiency andeconomics of their introduction into the thermoplastic material. Forexample, fine powders tend to be fairly readily dispersed but aredifficult to handle and can cause environmental problems. They are alsodifficult to introduce continuously into process equipment.

In practice, a number of procedures have been employed to incorporatesolid additives into polymeric systems. Conventional additive deliverysystems use dry additive feeding and mixing with polymer resins, inwhich dry plastic additives are metered and mixed with polymer particlesin blenders or mixers. Alternatively, dry additives are mixed with aresin as it is processed through a pelletizer, extruder, or compoundingdevice. In another process, the additives are melted and coated onplastic resin particles before introducing them into an extruder. Highmelting additives are difficult to control in this technology. In yetanother process, resin particles are coated with an aqueous emulsion ofthe additives, then dried. This procedure is not suitable forhydrolyzable additives such as many phosphite antioxidants, and thewater must ultimately be removed, resulting in complexity and expense.Other methods involve, for instance, dissolving additives in one or moreof the components of the mixture to be polymerized before the polymer isformed, or mixing the additive in a solution, suspension, or emulsion ofthe polymer and then removing the solvent or suspending agent.

The literature also contains descriptions of spray procedures forintroducing plastics additives into polymeric materials, and forspraying various other materials in supercritical carbon dioxide. Anumber of these references are discussed briefly below.

U.S. Pat. No. 5,007,961 and corresponding PCT application WO 90/02770disclose aqueous systems for applying additives to polymeric particles,as well as methods for applying such additive systems such as spraying,wiping, or dipping, and polymeric particles treated with such additivesystems. The additive systems comprise an emulsified wax, surfactant,base, one or more functional polymer additives, and water.

European patent application 411,628 discloses stabilizing polyolefins innon-extruded as-polymerized particle form by depositing on the particlesa mixture of stabilizers including one or more organic phosphites orphosphonites and one or more phenolic antioxidants. Optional ingredientsare thioethers, organic polysulfides, hindered amine light stabilizers,benzophenone and benzotriazole derivatives, and diluents such asparaffins, cycloparaffins, epoxidized soybean or linseed oil, siliconeoils, and olefin oligomers. The stabilizer mixtures are applied, in amelted state or in a liquid state by virtue of containing liquidphosphites or phosphonites, by a continuous or batch mixer optionallyequipped with a spraying mechanism.

U.S. Pat. No. 5,041,310 of Williams discloses a coating compositioncomprising a mixture of polymer additives, gelling agent, and oil, whichis applied as a liquid to the surface of particles of polymer, andcaused to gel.

U.S. Pat. No. 4,960,617 discloses a process for post-reactorstabilization of polyolefins by melting a polyolefin wax, blending atleast one additive into the resulting melt, fluidizing polyolefinparticles to be stabilized with hot gas, and spraying the liquidpolyolefin wax containing at least one additive on the fluidizedpolyolefin particles.

U.S. Pat. No. 4,882,107 discloses a method and apparatus for spraying asolution, suspension, or dispersion of a mold release material in asupercritical fluid such as supercritical carbon dioxide onto thesurface of a mold, to coat it with the release agent.

U.S. Pat. Nos. 4,923,720 and 5,027,742 and Chemical Abstract 113:154288pdisclose a process and apparatus in which supercritical fluids such assupercritical carbon dioxide are used to reduce the viscosities ofviscous coating compositions to permit their application as liquidsprays.

U.S. Pat. No. 5,066,522 discloses the use of supercritical fluids suchas supercritical carbon dioxide as diluents in liquid spray applicationsof adhesives.

European patent application 350,910 discloses liquid spray applicationof coatings with supercritical fluids as diluents, and spraying from anorifice.

Production of fine powders in inorganic oxides and certain drugs byrapid expansion of supercritical fluid solutions has been reported. SeeChemical Abstracts 108:155263k, 105:197085x, 105:63102s, and104:227104b. Graphite has also been produced in a micro-powder form bywetting it with liquid CO₂ then vaporizing the CO₂ at a temperature andpressure above the critical point of CO₂ gas. See Japanese patentpublication 62/265111. However, it does not appear that particle sizereduction of plastics additives in nonvolatile liquid matrices uponspraying in supercritical CO₂ has been reported.

Despite the progress made in applying polymer additives to polymers inspray processes, indicated by the references discussed above, prior artprocesses generally suffer from certain deficiencies. Some liquidsystems have high viscosities which make them difficult to atomizewithout heating, dilution, use of a high amount of atomization gas,and/or use of relatively high pressures for spraying. Systems whichinvolve the spraying of materials which are solids under standardconditions can experience difficulties related to handling or melting ofthe solids, and plugging of lines as a result of resolidification of thesolid materials in vessels, piping, and the spray nozzle. Suchoperational difficulties can make the spraying operation inefficient,adversely affecting not only its economics, but also the control of theamounts of the additives and the uniformity of their application to thepolymer being treated. An improved spray process for applying plasticsadditives to polymers would be very desirable. Such a process is thesubject of this application.

SUMMARY

The process of the present invention involves the steps of 1) forming ina closed pressurized system a mixture comprising: a) at least onepolymer additive material which is a solid under standard conditions oftemperature and pressure; b) at least one liquid carrier materialcapable of dissolving, suspending, or dispersing the polymer additivematerial; and c) at least one viscosity reducing material which is i) afluid under the pressure of the closed pressurized system, ii) at leastpartially soluble in the liquid carrier material, iii) present in themixture in an amount which is effective to cause the mixture to have aviscosity which renders it sprayable, and iv) volatile under standardconditions of temperature and pressure; and 2) spraying the mixture ontoa polymeric substrate.

This process enables manufacturers of plastic items to introducemixtures of plastics additives onto resins in a convenient liquid form,thereby avoiding the problems of handling, dusting, agglomeration, andmetering or measuring associated with dry solids. No volatile solvent orwater is incorporated into the polymeric substrate. Reduction of solidparticle size occurs upon spraying of a number of plastics additives.The spraying aspect of the process provides both improved control of theamounts of additives applied and the uniformity of their incorporationinto the polymer.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more completely understood from a consideration ofthe following detailed description taken in conjunction with thedrawing, in which:

FIG. 1 is a schematic diagram of apparatus which may be employed in thespray process of the invention; and

FIG. 2 is a schematic diagram of apparatus for continuous spraying.

DETAILED DESCRIPTION

Polymer additive materials, otherwise referred to as polymer additives,are materials which are suitable for inclusion in polymers to affecttheir properties or processing characteristics. In other words, they arecompounds which affect or modify the properties of a polymeric system ofwhich they are a part. Depending of their chemical constitutions, theymay act as antioxidants, neutralizers, metal or catalyst deactivators,slip agents, light stabilizers, antiblocking agents, colorants,lubricants, flame retardants, coupling agents, processing aids,antistatic agents, nucleating agents, blowing agents, etc.

Examples of antioxidants include, but are not limited to: hinderedphenols, phosphites, and propionates. Examples of hindered phenols are1,3,5-trimethyl-2,4,6-tris-(3,5-di-tert-butyl-4-hydroxybenzyl)benzene;octadecyl-3-(3,5-ditert-butyl-4-hydroxyphenyl)propionate; tetrakis[methylene-3(3',5'-di-tert-butyl-4'-hydroxyphenyl)-propionate]methane);4,4'-butylidene-bis(5-methyl-2-t-butyl)phenol; and2,2'-ethylidene-bis-(4,6-di-tert-butylphenol). Examples of phosphiteandioxidants are tris(2,4-di-tert-butyl-phenyl)phosphite;bis(2,4-di-t-butyl-phenyl) pentaerythritol diphosphite; and2,2'-ethilidene-bis(4,6-di-t-butylphenyl)fluorophosphite. Examples ofpropionate antioxidants are dilaurel thiodipropionate and distearylthiodipropionate.

Examples of neutralizers/catalyst deactivators include, but are notlimited to: zinc oxide, zinc stearate, fatty amines and fatty amidessuch as those sold by a division of Witco Chemical Company under theKEMAMINE label; 3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy-benzene propanoicacid; 2-[3[3,5-bis-(1,1-dimethylethyl)-4-hydroxyphenyl]-1-oxopropyl]hydrazide; molecular sieve, and hydrotalcites.

Examples of slip agents include, but are not limited to: erucamide,oleamide, and ethylene bis-stearamide.

Examples of light stabilizers include, but are not limited to:benzophenone stabilizers, such as those sold under the tradenamesCYASORB-UV 2018 (American Cyanamid), UVINUL M40 and UVINUL 490 (BASFCorporation), hindered amine compounds such as those containingtetraalkyl-piperidinyl functionality, including UV absorbers marketed byCiba Geigy under the tradenames TINUVIN 144, TINUVIN 326, TINUVIN 327,TINUVIN P, TINUVIN 622LD, and TINUVIN 770(N,N-diphenyl-N,N-di-2-naphthyl-p-phenylene-diamine), AmericanCyanamid's CYANOX 3346, and FAIRMONT MIXXIM AO-30.

Examples of blowing agents are: azodicarbonamide and sodium bicarbonate.An example of a nucleating agent is dibenzylidine sorbitol.

Examples of antiblocking agents are diatomaceous silica, clay, and talc.

Examples of colorants are titanium dioxide, carbon black, and organicdye pigments.

Examples of lubricants are organomodified polydimethylsilioxanes such asUCARSIL PA-1 processing aid and polyalkylene glycols such as UCON®lubricant LB-285, available from Union Carbide Chemicals and PlasticsCompany Inc., and calcium stearate.

Examples of processing aids are calcium stearate and organomodifiedpolydimethylsilioxanes such as UCARSIL® PA-1 processing aid.

Examples of antistatic agents are glycerol monostearates, etholatedamines, polyethylene glycol esters, and quaternary ammonium compounds.

Standard conditions of temperature and pressure means 25° C. and oneatmosphere pressure.

Liquid carrier materials useful in the process of the invention,otherwise referred to as liquid carriers, are materials which arecapable of dissolving, suspending, or dispersing polymer additives. Theymay be functional or nonfunctional fluids, and are substantiallynonvolatile under standard conditions of temperature and pressure.

Examples of functional liquid carriers are organomodified polysiloxanessuch as Union Carbide's UCARSIL® PA-1 processing aid, liquid phosphitestabilizers such as Borg Warner's WESTON 399B, alpha tocopherol (vitaminE), ditridecylthiopropionate, trisnonylphenylphosphite, ethoxylatedfatty amines, alkylated diphenylamines, and alkyllauryl polyetherphosphate esters. Examples of nonfunctional liquid carriers include, butare not limited to: polyethers such as polyethylene glycols andpolyalkylene glycol lubricating oils such as Union Carbide's UCON®lubricant LB-285; hydrocarbons such as mineral oils, poly alpha olefins,polypropylene oils; and polyesters such as sorbitan monooleate andglycerol trioleate. These are relatively low surface energy materials.

Viscosity reducing materials suitable for use in this invention arecompressed fluids such as supercritical fluids and subcriticalcompressed fluids.

As used herein, the term "compressed fluid" means a fluid which may bein its gaseous state, its liquid state, or a combination thereof, or isa supercritical fluid, depending upon (1) the particular temperature andpressure to which it is subjected upon admixture with the solvent-bornecomposition that is to be sprayed, (2) the vapor pressure of the fluidat that particular temperature, and (3) the critical temperature andpressure of the fluid, but which is in its gaseous state at the standardconditions of zero degrees Celsius temperature and one atmosphereabsolute pressure. As used herein, a "supercritical fluid" is a materialthat is at a temperature and pressure such that it is at, above, orslightly below its critical point. As used herein, the critical point isthe transition point at which the liquid and gaseous states merge intoeach other and represents the combination of the critical temperatureand critical pressure for a given substance. The critical temperature asused herein is defined as the temperature above which a gas cannot beliquefied by an increase in pressure. The critical pressure as usedherein is defined as that pressure which is just sufficient to cause theappearance of two phases at the critical temperature.

Examples of viscosity reducing materials which may be employed assupercritical fluids in the process of the invention include, but arenot necessarily limited to, carbon dioxide, ammonia, nitrous oxide,xenon, krypton, chlorotrifluoromethane, monofluoromethane, methane,ethane, ethylene, propane, and pentane. The critical parameters of thesematerials are listed in Table 1.

                  TABLE 1                                                         ______________________________________                                        Critical Parameters of Supercritical Fluids                                             Boiling   Critical  Critical                                                                             Critical                                           Point     Temp.     Pressure                                                                             Density                                  Compound  (°C.)                                                                            (°C.)                                                                            (bar)  (g/ml)                                   ______________________________________                                        Carbon Dioxide                                                                          -78.5     31.3      72.9   0.448                                    Ammonia   -33.35    132.4     112.5  0.235                                    Nitrous Oxide                                                                           -88.56    36.5      71.7   0.45                                     Xenon     -108.2    16.6      57.6   0.118                                    Krypton   -153.2    -63.8     54.3   0.091                                    Chlorotrifluoro-                                                                        -31.2     28.0      38.7   0.579                                    methane                                                                       Monofluoro-                                                                             -78.4     44.6      58.0   0.3                                      methane                                                                       Methane   -164.0    -82.1     45.8   0.2                                      Ethane    -88.63    32.28     48.1   0.203                                    Ethylene  -103.7    9.21      49.7   0.218                                    Propane   -42.1     96.67     41.9   0.217                                    Pentane   36.1      196.6     33.3   0.232                                    ______________________________________                                    

Examples of viscosity reducing materials which may be employed as highpressure subcritical compressed fluids include, but are not necessarilylimited to, carbon dioxide, ammonia, nitrous oxide, xenon,chlorotrifluoromethane, monofluoromethane, ethane, and propane.

Carbon dioxide (CO₂) and nitrous oxide (N₂ O) are preferred viscosityreducing materials for the practice of the present invention due totheir low critical temperatures, low toxicities, nonflammability, andlow cost. Carbon dioxide is the most preferred viscosity reducingmaterial because of its low cost, availability, and environmentalacceptability. Mixtures of any of the above mentioned materials are alsowithin the scope of the invention.

The purpose of the viscosity reducing material is to reduce theviscosity of the mixture of polymer additive and liquid carrier to apoint where it is sprayable, thus permitting relatively high levels ofadditives to be used in the composition to be sprayed, and to providethis function in an environmentally benign way. To fulfill thisfunction, the viscosity reducing material must be a fluid under thesystem conditions of temperature and pressure, at least partiallysoluble in the liquid carrier, and present in an effective amount. Sinceit is not intended that the viscosity reducing material become part ofthe treated plastic, it should be volatile.

The step of spraying may be accomplished using any appropriate equipmentcapable of handling and spraying mixtures of liquids and solids underpressure.

The process of the invention may be employed to introduce plasticsadditives into or onto any polymeric material, those with low surfaceenergies being preferred. Examples of polymeric materials which may betreated are the following: polyolefins such as high density polyethylene(HDPE), linear low density polyethylene (LLDPE), low densitypolyethylene (LDPE), polypropylenes, polyacrylates andpolymethacrylates, poly(vinyl chloride), and polystyrene; polyesters;polyamides such as nylons; cellulose acetates; polycarbonates; andcrystalline and elastomeric copolymers of ethylene with propylene and/orother C₃ -C₈ straight or branched chain alpha olefins such as 1-butene,1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, 3-methyl-1-butene;terpolymers of alpha olefins and dienes; acrylonitrile-butadiene-styreneterpolymers; heterophasic polymers of propylene and other olefinpolymers and/or copolymers; and mixtures thereof. Numerous othermaterials will occur to those skilled in the art. The process is mostuseful for introducing additives into polymeric materials which are insolid form, and preferably in particulate form.

FIG. 1 shows a schematic diagram of apparatus suitable for practicingthe spraying process of the invention in a batch mode. A pressurizablemixer 10 is equipped with means for mixing 12 which may be driven by amotor 14. Pressurizable mixer 10 is additionally provided with heatingmeans 16. Attached to mixer 10 via lines 18, 20, and 22 is a tank 24 forholding a mixture of materials to be sprayed. Tank 24 is provided withan air inlet 26 and a vent 28. A pump 30 such as a gear pump is providedbetween lines 20 and 22 to move material to be sprayed from tank 24 intomixer 10. Also attached to mixer 10 is a container 32 of viscosityreducing material, container 32 being connected via line 34 to a gasbooster pump 36, the output of which is connected via line 38 to a surgetank 40, which is in turn connected via line 42 to a liquids pump 44whose output is connected via line 46 to a second surge tank 48, theoutput of which is connected via line 50 to line 18 and thence intomixer 10. Mixer 10 may optionally be provided with a recirculating loopshown in the figure by lines 52, 54, and 56. Pump 58 is provided in therecirculation loop for recirculating the contents of mixer 10, andsprayer 60 is connected to the recirculation loop via lines 62 and 64.Mixer 10 is also provided with pressurization means 66, such as, forinstance, a source of nitrogen gas. If a recirculating loop is not used,mixer 10 is connected to sprayer 60 via lines 56 and 64 and valve 74,and lines 52, 54, pump 58, and values 68, 70 and 72 are either absent orshut down.

FIG. 2 shows an alternative spraying apparatus, for continuous spraying.In this unit a jacketed static mixer 80 is employed for mixing theadditive slurry with the viscosity reducing material. Following mixer 80is an air driven power mixer 82 which is in turn connected to sprayer60, which in this instance is controlled by an air operated solenoid andtimer 84. Depending on the material being sprayed, it may only benecessary for the spray apparatus to possess one mixer, 80 or 82. In asingle mixer apparatus, mixer 80 is preferred. As before, the mixture ofmaterials to be sprayed is held in tank 24, which is provided with aninlet 26 and a vent 28. Tank 24 is connected via line 22 to pump 30,which is in this instance connected to a variable speed drive 86. Theoutlet of pump 30 connects to line 20, which is in turn connected tostatic mixer 80. A container 32 of viscosity reducing material isconnected via line 88 to the inlet of an air driven gas booster pump 90,which is in turn connected to a small surge tank 92, which is connectedto an air driven liquids pump 94 via line 96. This is in turn connectedto a second small surge tank 98 which is connected via line 100 to aneedle valve 102. The exit side of needle valve 102 is connected vialine 104 to a back pressure regulator 106, which is in turn connectedvia line 108 to line 20 leading into static mixer 80.

Examples of processing equipment used for mixing include, but are notlimited to, static mixers, power mixers, and other mechanical mixingdevices, as well as recirculators for use with a closed system. Examplesof mechanical mixing devices are the Kenics Static Mixer model 37-08-135and the Graco Hydra-Cat Power Mixer model 207-388 series F. Pumps 30 and58 are preferably gear pumps such as those made by Viking and Zenith.Pumps 36 and 44 of FIG. 1 correspond to pumps 90 and 94 of FIG. 2. Thegas booster pumps 36 and 90 are preferably air driven gas booster pumpssuch as those made by Haskel. Liquids pumps 44 and 94 are alsopreferably but not necessarily air driven. Heating of process fluids canbe provided for in any of the various ways known to the art, or in thecase of a static mixer, a heating jacket may be employed as illustrated.Close coupling of the mixing apparatus to the spraying operation ispreferred to maintain well mixed fluid for spraying. This isparticularly important when the viscosity reducing material is used inan amount higher than is soluble in the mixture of polymer additive andliquid carrier.

Examples of spray units include, but are not limited to, the pluralcomponent or airless types manufactured by Binks, Nordson, Graco, andSpraying Systems.

Examples of apparatus which may be employed to handle the polymericmaterials being spray treated include ribbon blenders, Henshall mixers,a resin drop zone, and a conveying line.

Referring to FIG. 1, in practice, one or more polymer additive materialsare suspended or dispersed in a liquid carrier material to form amixture having a paste-like consistency. This is initially charged totank 24, from which it is conveyed through lines 22, 20, and 18 intomixer 10. Mixer 10 is sealed and pressurized, and viscosity reducingmaterial from container 32 is introduced to mixer 10 under pressure andthere mixed with the polymer additive material and liquid carriermaterial to form a sprayable composition. Spraying may be carried outwith or without the circulating loop. Where the circulating loop isemployed, valves 68, 70, and 74 are open and valve 72 is closed. Whenthe circulating loop is not employed, valves 68, 70, and 72 are closedand valve 74 is open.

The operation of the apparatus shown in FIG. 2 is substantially similarto that of FIG. 1, except that the materials to be sprayed are providedcontinuously to mixers 80 and/or 82. The viscosity reducing material,preferably CO₂, is preferably supplied as a liquid from any suitablesource, such as a cylinder or tank. It is pressurized by the gas boosterpump, then pressurized by the liquids pump to a final desired pressure.Surge tanks are placed in the delivery line to dampen the flow andpressure pulsations resulting from intermittent flow from thereciprocating pump. The flow rate of the viscosity reducing material isadjusted by setting the air pressure to the liquids pump, adjusting theneedle valve 102, and adjusting the back pressure to control the flowthrough the needle valve. The back pressure regulator is adjusted abovethe desired spraying pressure to allow for CO₂ delivery and mixing withthe slurry. Additional apparatus for measuring and controlling CO₂ flowrate to the system may also be included.

Low average spraying rates using the apparatus of FIG. 1 or FIG. 2 canbe maintained by intermittent spraying, rapidly opening and closing thespray orifice in sprayer 60, as illustrated in FIG. 2. Such intermittentoperation of the sprayer can be achieved by air operated solenoids orelectronic solenoids in an automatic spray gun assembly. Cycle rates of180 cycles per minute are commercially available with air operatedsolenoids, and cycle rates up to 1800 cycles per minute are commerciallyavailable with electronic solenoids. Sprayers with good positive shutoffcontrol are preferred for this intermittent mode of operation.

In the inventors' experience, a Nordson automatic spray gun gives themost preferred intermittent spray operation.

Upon being sprayed in accordance with the process of the invention, manyof the solid polymer additive materials undergo substantial particlesize reduction, which improves the potential for obtaining uniformcoatings of the additives on polymer particles being treated. Thesuperior dispersion ultimately achieved in the resin enables the desireddegrees of polymer stabilization to be achieved at lower levels of addedstabilizers than would be required if the stabilizers were added byother means.

An alternative means for providing finely divided solid additives forcoating polymer particles is to subdivide the additive materials in aprocess such as dry or wet milling prior to spraying them onto thepolymer. However, pumpable slurries containing small particle sizesolids are more viscous than slurries containing an optimized sizedistribution of solid particles, thus presenting practical difficultiesin conveying slurries containing high concentrations of such smalladditive particles. The additive particle size reduction which can beachieved for many solid plastics additives in the process of thisinvention thus allows for delivery of additive mixtures in which theinitial slurry can be optimized for maximum solids loading, whileultimately producing spray which contains solid particles of plasticsadditives in a much reduced particle size.

The process of the invention is not restricted to mixtures of onepolymer additive, one liquid carrier material, and one viscosityreducing material. The ultimate mixture to be sprayed onto the polymericsubstrate may include multiple solid plastics additives, multiple liquidcarrier materials, and multiple viscosity reducing materials. It mayalso optionally include one or more liquid additive components. Themixture to be sprayed may originate as one or more stable slurries ofplastics additives and liquid carrier materials, which are combined toform the ultimate sprayable mixture. When several slurries of additivesare to be combined, this may readily be accomplished by having each in aseparate holding tank and introducing it via its own pumping system andtransfer line. Other variations on the theme will occur to those skilledin the art.

The pressure to be employed in the process of the invention needs to behigh enough to allow production of a thinned effervescent spray from theadditive mixture. Operating pressure may be in the range of 13.8 to 346bar, preferably 35.5 to 208 bar, and most preferably 49.3 to 139 bar.

The temperature to be employed in the process may range from ambient tothe stability limit of the materials being sprayed, preferably fromambient temperature to 100° C., and most preferably from ambienttemperature to 60° C. Increasing temperature reduces the viscosity ofthe mixture to be sprayed, thus increasing the spray quality.

The concentration of solid plastics additives in the slurry of additiveand liquid carrier material, prior to addition of the viscosity reducingmaterial, may range from low values such as 5% by weight, to as high asapproximately 70% by weight. Slurries containing solids loadings above70% by weight are not readily pumped or metered. Slurries containing lowsolids concentrations need to be manufactured in a form that isgravametrically stable or settling and variation of mixtureconcentrations can result. Alternatively, unstable suspensions can bemixed just prior to spraying. The preferred range of solidsconcentrations for the slurry is 15% to 70% by weight, and the mostpreferred range is 25% to 65% by weight.

The size of the spray nozzle of sprayer 48 needs to be large enough toallow slurry particles to pass through without plugging. The minimumnozzle size will depend on the size of the largest particles in theslurry. Large orifice nozzles are preferred to minimize the chance fororifice plugging, and to allow for spraying of slurries which containlarge particles. Smaller orifice sizes are preferred for maintaining lowcontinuous flow rates. The spray nozzle orifice may typically be in therange of 0.13 to 5.1 mm; more typically it will be in the range of 0.18to 2.5 mm.

The particle size of the polymer additive materials employed in theprocess can range from less than 1 micron to 2,000 microns, preferablyfrom less than 1 micron to 1,000 microns, and most preferably is lessthan 1 to 200 microns. A slurry mixture containing the proper ratio ofcoarse to fine particles allows for the highest concentration slurrythat can be pumped or will flow. Very coarse materials will plug nozzlesand should be avoided. If the particle size of the polymer additivematerial is too large, the additive should be milled or micronized orotherwise reduced in particle size.

The concentration of the viscosity reducing material to be employed inthe process of the invention needs to be high enough to allow sprayingof the mixture of polymer additive material and liquid carrier. Thisamount will increase with increasing solids concentration and decreasingtemperature. The mixture to be sprayed may contain viscosity reducer atlevels above the solubility limit of the viscosity reducer in themixture of the polymer additive and liquid carrier. The solubility limitof the viscosity reducer and the additive mixture will depend on severalparameters, including the solids concentration, liquid carrier type,temperature, and pressure. In general, the viscosity reducing materialmay be employed at levels from 0.05 to 5 kg per kg of the additivemixture to be sprayed, preferably 0.10 to 1 kg per kg of additivemixture to be sprayed, and most preferably from 0.15 to 0.6 kg per kg ofthe mixture to be sprayed.

EXPERIMENTAL Listing of Chemicals and Equipment

The model SS-1ST 3000 Test Cell was purchased from J. M. CantyAssociates, Inc., 117 Cornwall Avenue, Tonawanda, N.Y. 14150.

Carrier Liquid 1 was UCARSIL® PA-1 processing aid, which is anorganomodified polydimethylsiloxane manufactured by Union CarbideChemicals and Plastics Company Inc.

Carrier Liquid 2 was UCON® LB-285 lubricant, which is a polyalkyleneglycol available from Union Carbide Chemicals and Plastics Company Inc.

Vitamin E was purchased from Aldrich and was 97% pure.

Antioxidant 1 is a substituted phenol, more particularly,1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxy-benzyl)benzene,available from Ethyl Corporation.

Antioxidant 2 is a substituted phenol, more particularly,2,2'-ethylidene-bis(4,6-di-tert-butylphenol), available from SchenectadyChemicals, Inc.

Stabilizer 1 is a phosphite, more particularly,tris-(nonylphenyl)phosphite with triisopropanolamine stabilizer,available from Borg-Warner Corporation.

Stabilizer 2 is a phenol, more particularly,tetrakis[methylene-3(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate]methane,available from Ciba Geigy.

Stabilizer 3 is a is a phosphite, more particularly,tris-(2,4-di-tert-butylphenyl) phosphite, available from Ciba GeigyCorporation.

Stabilizer 4 is a phosphite, more particularly,bis-(2,4-di-tert-butlyphenyl) pentaerythritol diphosphite, availablefrom Borg-Warner Corporation.

Stabilizer 5 is a substituted phenol, more particularly,octadecyl-3,5-di-tert-butyl-4-hydroxyhydrocinnamate, available from CibaGeigy Corporation.

The particle analyzer was a Leeds and Northrup Microtrac™ FRA, whichoperates on the principle of laser diffraction and Mie light scattering.

EXAMPLE 1 Solubility of CO₂ in Carrier Liquid 1

Solubility of CO₂ in Carrier Liquid 1 was determined with a model SS-1ST3000 test cell from J. M. Canty Associates, Inc. This test cell includesa high pressure viewing port and is rated at 3000 psig (207.9 bar). Thetest cell was charged with 25.4 grams of Carrier Liquid 1, liquid CO₂was added at room temperature (25° C.) until two separate liquid phaseswere observed through the cell's viewing port sight glass, and then thecell was vented until a single liquid phase remained. The test cell wasnext slowly depressurized through a wet test meter used to determine gasflow. A CO₂ solubility of 30-40 weight percent in the Carrier Liquid 1was estimated from this procedure. In addition, a volumetric increase ofabout 50% relative to the untreated Carrier Liquid 1 was observed forthe single liquid phase.

EXAMPLE 2 Solubility of CO₂ in Various Liquids at Room Temperature

Solubility of CO₂ in several additional liquids were measured as inExample 1. The liquids tested include Union Carbide's PEG-400polyethylene glycol, Carrier Liquid 2, Vitamin E, and Stabilizer 1. Eachof the liquids tested showed a CO₂ solubility in the range from 20-35weight percent at room temperature and at the pressure where only oneliquid phase was observed in the test cell.

EXAMPLE 3 Viscosity Reduction Trial with a Mixture of Stabilizers

A slurry of 22 wt. % of Stabilizer 2, 43 wt. % of Stabilizer 3, and 35wt. % of Carrier Liquid 1 was placed in the test cell, CO₂ was added,and the temperature in the cell was raised to 32° C., a point where asecond CO₂ -rich phase was not observed in the test cell. The slurryphase thinned significantly so that it could now be agitated like aliquid. From observing the slurry, it was judged that pumping could beaccomplished. Spraying feasibility was not determined from these visualobservations.

EXAMPLE 4 Spraying Trials

A plastic additives batch spray test apparatus according to FIG. 1 wasused for determining the feasibility of spraying plastic additives usinghigh pressure CO₂. The first test was carried out with a mixture of 2050g of Carrier Liquid 2 and 570 g of coarsely ground Stabilizer 2. Theparticle size of the coarsely ground material was about 25-30 microns.This mixture was placed in the autoclave, 940 g of CO₂ was added, andthe mixture was heated to 50° C. The spraying temperature was 47° C. andspray pressure was maintained at 1230 psig (85.8 bar). A 0.33 mm orificespray tip (Binks 013-150025) functioned well with the above operatingconditions. A second spray nozzle (Binks 9-1360) of 0.23 mm orifice alsofunctioned satisfactorily. A spray rate of 41 pounds per hour (18.6 kgper hour) was measured using the 0.23 mm spray nozzle.

EXAMPLE 5 Additional Spraying Trials

Several additional slurry recipes were made and tested in the batchspray test apparatus used in Example 4. The table 2 below gives asummary of the test results. In general, spraying became difficult assolids concentration increased, pressure decreased, temperaturedecreased and spray nozzle size decreased. Spray rates for severaloperating conditions were measured on a CO₂ -free basis by collectingsprayed material in a vented 5 gallon (18.9 liter) plastic container.

                                      TABLE 2                                     __________________________________________________________________________    Spraying Trials                                                                          Particle  Orifice                      Spray                       %   Solid  Size  Carrier                                                                           Size                                                                              Nozzle   Temp.                                                                             Pressure    Rate                        Solids                                                                            Materials                                                                            (Microns)                                                                           Liquid                                                                            (mm)                                                                              Designation                                                                            (°C.)                                                                      (bar)                                                                              Sprayable?                                                                           (kg/hr)                     __________________________________________________________________________    22  Stabilizer 2                                                                         25    2   0.23                                                                              Binks 9-1360                                                                           48  87.2 YES    19.1                        22  Stabilizer 2                                                                         25    2   0.33                                                                              Binks 013-150025                                                                       48  87.2 YES                                50  Stabilizer 2                                                                         25    2   0.33                                                                              Binks 013-150025                                                                       48  92.4 NO                                 50  Stabilizer 2                                                                         25    2   0.43                                                                              Graco 163-317                                                                          48  96.9 YES                                50  Stabilizer 2                                                                         25    2   0.38                                                                              Graco 163-315                                                                          48  96.9 YES                                50  Stabilizer 2                                                                         25    2   0.38                                                                              Graco 163-315                                                                          32  78.9 YES    25.9                        50  Stabilizer 2                                                                         25    2   0.38                                                                              Graco 163-315                                                                          43  72.0 YES    20.9                        50  Stabilizer 2                                                                         25    2   0.38                                                                              Graco 163-315                                                                          41  56.9 PLUGS                              65  Stabilizer 2                                                                         25    2   0.43                                                                              Graco 163-317                                                                          44  88.9 PLUGS                              65  Stabilizer 2                                                                         25    2   0.51                                                                              Graco 163-820                                                                          44  88.9 YES                                65  Stabilizer 2                                                                         25    2   0.79                                                                              Graco 163-431                                                                          44  88.9 YES                                  28.3                                                                            Stabilizer 2                                                                         25    1   0.23                                                                              Binks 9-1360                                                                           46  96.2 YES                                  28.3                                                                            Stabilizer 2                                                                         25    1   0.33                                                                              Binks 013-150025                                                                       46  96.2 YES                                  62.5                                                                            Stabilizer 2                                                                         25    1   0.43                                                                              Graco 163-317                                                                          56  87.9 YES    43.2                          62.5                                                                            Stabilizer 2                                                                         25    1   0.51                                                                              Graco 163-820                                                                          56  92.0 YES    33.6                        60  Mix 1  100   1   0.38                                                                              Graco 163-315                                                                          53  92.0 NO                                 60  Mix 1  100   1   0.43                                                                              Graco 163-317                                                                          53  90.7 YES    41.8                        60  Mix 1  100   1   0.43                                                                              Graco 163-317                                                                          46  90.7 YES    53.8                        60  Mix 1  100   1   0.43                                                                              Graco 163-317                                                                          37  70.3 NO                                 60  Mix 1  100   1   0.79                                                                              Graco 163-431                                                                          39  71.3 YES    66.4                        __________________________________________________________________________    70  Antioxidant 2                                                                              1   0.79                                                                              Graco 163-481                                                                          52  105.1                                                                              YES                                70  Antioxidant 2                                                                              1   0.43                                                                              Graco 163-317                                                                          52  105.1                                                                              NO     see (1)                     60  Mix 1  100   1   0.43                                                                              Graco 163-317                                                                          43  94.1 YES    37.3                        60  Mix 1  100   1   0.38                                                                              Graco 163-317                                                                          45  72.0 PLUGGED                            60  Stabilizer 2                                                                         100   1   0.79                                                                              Graco 163-431                                                                          46  76.9 YES    see (2)                     30  Stabilizer 2                                                                         100   1   0.79                                                                              Graco 163-431                                                                            38.5                                                                            104.5                                                                              YES    88.2                        31  Stabilizer 2                                                                         100   1   0.51                                                                              Graco 163-820                                                                            38.5                                                                            104.5                                                                              NO                                 55  Antioxidant 1                                                                        100   2   0.48                                                                              Graco 163-619                                                                          38  85.1 NO                                 55  Antioxidant 1                                                                        100   2   0.79                                                                              Graco 163-431                                                                          40  88.6 YES                                50  Mix 2        1   0.48                                                                              Graco 163-619                                                                          44  103.1                                                                              YES                                50  Mix 2        1   0.79                                                                              Graco 163-431                                                                          40  80.3 YES                                50  Mix 2        1       Nordsen 30.08                                                                          47  75.5 YES    44.1                        50  Mix 2        1       Nordsen 20.12                                                                          54  76.9 YES    28.2                        __________________________________________________________________________     Mix 1 Composition contains:                                                   37.3% Stabilizer 2                                                            22.7% Stabilizer 4                                                            40% Carrier Liquid 1                                                          (1) Spray gun plugged behind seat and not in nozzle. High solids for batc     device.                                                                       (2) Significant buildup in autoclave.                                         (3) Mix 2 slurry contains:                                                    25% Stabilizer 2 (Unground)                                                   25% Stabilizer 3 (Unground)                                                   50% Carrier Liquid 1                                                     

EXAMPLE 6 Demonstration of Low Average Flow Rate Using IntermittentSpraying

Spraying trials with solid antioxidants were conducted using an airoperated spray gun operated in an intermittent spraying mode (Binksmodel 560, or a Nordsen air operated assembly). The opening and closingof the spray aperture was controlled by a three way solenoid valveattached to an ON/OFF timer. Average rates of spraying were establishedby selecting various values of the ON and OFF settings on the timer.Representative rates for several tests are summarized in Table 3 below.The spray assembly operated effectively without shutoff leakageproblems. It is seen that low average spraying rates can be achievedreadily by selecting appropriate settings on the ON/OFF timer.

                  TABLE 3                                                         ______________________________________                                              Spray            ON    OFF   Spray  Spray                                     Temp    Pressure Time  Time  Tip Size                                                                             Rate                                Sample                                                                              (°C.)                                                                          (bar)    (sec) (sec) (mm)   (kg/hr)                             ______________________________________                                        Mix 3 45      89.3     0.25  1     0.43   10.0                                Mix 3 45      82.4     0.25  1     0.48   10.5                                Mix 3 45      88.6     0.10  1     0.48    5.0                                Mix 4 45      88.6     cont. --    0.46   35.2                                Mix 4 46      94.8     0.10  1     0.46    3.7                                Mix 5 47      94.8     0.25  1     0.38    5.6                                Mix 5 49      90.7     0.25  1     0.43    8.9                                Mix 5 47      107.2    0.25  1     0.43   12.2                                Mix 6 48      85.1     0.3     0.75                                                                              0.38    7.2                                Mix 6 48      85.1     cont. --    0.38   23.6                                Mix 6 48      90.7     cont. --    0.48   33.9                                ______________________________________                                         Footnotes for Table 3:                                                        a) Mix 3 is 40% Carrier Liquid 2, 30% Stabilizer 2, and 30% Stabilizer 3,     by weight.                                                                    b) Mix 4 is 45% Carrier Liquid 2, 27.5% Stabilizer 2, and 27.5% Stabilize     3, by weight.                                                                 c) Mix 5 is 50% Carrier Liquid 2 and 50% Stabilizer 2, by weight.             d) Mix 6 is 40% Carrier Liquid 1, 37% Stabilizer 2, and 23% Stabilizer 4,     by weight.                                                               

EXAMPLE 7 Demonstration of Particle Size Reduction of Stabilizer 2 UponSpraying

It was qualitatively observed that after spraying a slurry of Stabilizer2 in the batch spray equipment with CO₂, the sprayed slurry was changedphysically from the initially charged feed slurry. The feed slurry wasgritty and contained relatively large irregular additive particles,whereas the sprayed material was very smooth and creamy in texture. Afurther test was conducted to determine the particle sizes in the feedand sprayed additive slurries. A slurry mixture was made as follows:

    ______________________________________                                                                 Concentration                                        Component      Weight (g)                                                                              (wt. %)                                              ______________________________________                                        Stabilizer 2   1200      30                                                   (unground)                                                                    Stabilizer 2   1200      30                                                   (coarse ground)                                                               Carrier Liquid 2                                                                             1600      40                                                   ______________________________________                                    

Samples of this mixture were diluted with dodecane and then analyzed forsolids particle size using a Microtrac particle size analyzer. Dodecanewas chosen as it was miscible with the Carrier Liquid 2 lubricant fluidand did not dissolve the solid additive particles. The feed materialshowed a bimodal particle size distribution with 35-45% of the particlesabove 100 microns in size and the bulk of the material having particlesizes of 25 to 100 microns. The samples were sprayed using the batchspray apparatus operating at 49° C. and 1275 psig (88.9 bar) through an18 mil (0.46 mm) orifice. The collected sprayed material was very smoothand creamy and contained only 1-2% of material with a particle sizelarger than 100 microns; the particle size of the bulk of the sprayedmaterial was in the range of 2-6 microns, as measured by the Microtracparticle size analyzer. The 50% cumulative volume particle size wasreduced from 67-80 microns for the feed to 8-10 microns for materialsprayed after 15 minutes circulation in the batch spray device.

Similar particle size reductions were observed for several additionalsolid plastic additive materials in the high pressure spray apparatuswith CO₂. Materials with which size reduction upon spraying occursinclude Stabilizer 2, Antioxidant 2, stabilizer 3, Stabilizer 4, andstabilizer 5.

EXAMPLE 8 Particle Size Reduction Trial of Antioxidant 1 Upon Spraying

A particle size reduction test was conducted for Antioxidant 1 inCarrier Liquid 2. A mixture containing 55% Antioxidant 1 (unground) andCarrier Liquid 2 was made and 3017 grams of the mixture was placed inthe batch spray apparatus autoclave. The mixture was heated to 40° C.while stirring in the autoclave and system pressure was maintained at1270 psig (88.6 bar) with CO₂. A total of 2100 grams of the test mixturematerial was sprayed through a spray nozzle to a collection jug. Thecollected sprayed slurry retained the gritty consistency characteristicof the feed slurry. Analysis of samples of the feed mixture and thesprayed material with the Microtrac particle size analyzer confirmedthat no substantial overall reduction in particle size of theAntioxidant 1 had occurred upon spraying, though the numbers ofparticles in the size range 300 to 600 microns were much reduced. TheCO₂ spraying system was not effective for reducing particle size ofAntioxidant 1. The Antioxidant 1 particles are harder and more densethan Stabilizer 2 particles and several other solid additive materials.

EXAMPLE 9 Particle Shearing in a Power Mixer

Shear tests using an air driven power mixer, appended to the apparatusof FIG. 1, located in the feed line leading to the sprayer downstream ofthe stirred autoclave and before the sprayer, were carried out tofurther evaluate the impact of mechanical agitation, N₂, and CO₂ have onreduction of additive slurry particle size. The recirculation loop wasnot used. Four sets of tests were carried out using nitrogen and CO₂ forpressurizing/mixing in the autoclave prior to passing the test mixturesthrough the power mixer and a 41 mil drilled orifice. The power mixer(Graco model #207-388 with mixing assembly #207-390 (3 blades)) providedhigh shear mixing. The mixer was driven with compressed air and themixer blades rotate at speed up to 2800 RPM. The chamber holding themixing blades has a 2.1 cubic inch (34.4 cubic centimeter) volumeholdup.

A total of 2700 grams of a mixture containing 25% of Stabilizer 2, 25%of Stabilizer 3 and 50% Carrier Liquid 1 was charged to the autoclave,the autoclave was pressurized to 1000 psig (70.0 bar) with nitrogen, andthe mixture was agitated two minutes in the autoclave with the autoclavemixer. The pressurized mixture was then allowed to pass through thepower mixer (mixing blades not on) and was sprayed through the 41 mil(1.04 mm) orifice. A sample of slurry was collected as it wasdischarging from the orifice. Next, the power mixer was turned on and asecond sprayed sample was collected. Both collected samples retained thegritty character of the feed material charged to the autoclave. The highspeed mixing had little impact on slurry characteristics.

The nitrogen pressure on the autoclave was slowly released and CO₂ wasadded to the autoclave to give a pressure of 1000 psig (70.0 bar). Theagitator in the autoclave was operated again for 2 minutes before thematerial was discharged through the orifice. Samples obtained with andwithout the power mixer running were both very smooth and creamy,indicative of significant size reduction of the solid additiveparticles. It is thus seen that a viscosity-reducing material such asCO₂, having the properties defined herein, is a preferred component forproducing a spray which gives reduced additive particle size.

EXAMPLE 10 Demonstration of Slurry Spraying in a Continuous Feed, HighPressure Spray

A high pressure spray device was constructed to demonstrate sprayoperation when additive slurry and CO₂ are continuously fed and sprayed.The equipment used for the demonstration is shown in FIG. 2. Theadditive slurry was fed from a holding tank 24 to a gear pump 30 capableof 1500 psig (104.5 bar) pressure. The slurry was then combined with CO₂and mixed in a 12 inch (30.5 centimeter) Kenics static mixer 80 prior tobeing sprayed. The initial demonstration tests were carried out atambient temperature without additional heating. The spray apparatus wasoperated with the air driven power mixer 82 alternately on and off. Aslurry containing 12.5% Stabilizer 2, 12.5% Stabilizer 3 and 75% CarrierLiquid 1 was mixed and placed in the feed tank 24. Other equipmentparameters and operating conditions are listed below:

1) Slurry pump speed: 5 rpm

2) Slurry pump discharge pressure: 900-1250 psig (63.1-87.2 bar)

3) CO₂ pump pressure: 900-1200 psig (63.1-83.8 bar)

4) Temperature: Ambient (28° C.)

5) Spray tip: Graco 431 (0.79 mm orifice)

6) The spray gun was controlled with an air operated solenoid valve 84.

7) Timer setting for air solenoid: 0.2 sec ON, 0.35 sec OFF.

The intermittent operation of the spray gun resulted in pressure swings.These fluctuations in system pressure can be reduced by sprayingcontinuously and/or by adjusting the surge capacity of the devicedownstream of the CO₂ and slurry mixing point. No significant differencein performance was observed when the power mixer was turned on. Observedspray quality was slightly better when the power mixer is turned on. Thecollected spray was smooth and creamy, again indicating a size reductionof solid additive particles during spraying.

EXAMPLE 11 Determination of CO₂ Solubility in Carrier Liquid 1

CO₂ solubility in the Carrier Liquid 1 portion of a slurry to be sprayedwas determined by collecting spray exiting the spray nozzle in the highpressure batch spray device of FIG. 1. The spray nozzle was placed intoa 5 gallon (18.9 liter) plastic jug and a vent line from the 5 gallon(18.9 liter) jug allowed evolved CO₂ to pass through a wet test meterwhere CO₂ gas volume was measured. Conditions for operation and CO₂usage are given below:

Autoclave pressure: 1045 psig (73.1 bar)

Autoclave temperature: 54-55° C.

Recirculation pump discharge pressure: 1200 psig (83.8 bar)

Spray gun temperature: 50-51° C.

Slurry:

Stabilizer 2: 25% (unground)

Stabilizer 3: 25% (unground)

Carrier Liquid 1: 50%

Results are shown in Table 4 below.

                  TABLE 4                                                         ______________________________________                                        Grams    Volume CO.sub.2                                                      slurry   collected             Grams CO.sub.2 per                             collected                                                                              (liters)              gram slurry                                    ______________________________________                                        88       9.12                  0.184                                          86       9.00                  0.185                                          82       8.35                  0.180                                          86       8.72                  0.179                                                                Average: 0.182                                          ______________________________________                                    

The CO₂ measured compares favorably with what is expected to be solublein the liquid portion of the slurry at operating conditions in theautoclave.

EXAMPLE 12 Effect of Varying the Amount of CO₂

The continuous spray apparatus of FIG. 2 was operated with varyingratios of CO₂ to additive slurry. A mixture of 50% carrier liquid 1, 25%stabilizer 2, and 25% of stabilizer 3, by weight, was employed for theadditive slurry. Mixing was provided for several tests with a powermixer operating at high rpm just upstream of the spray assembly. CycledON/OFF spraying was used to allow for a low overall spraying rate fromthe assembly. A summary of operating conditions and ratios of CO₂ toslurry is given in Table 5 below. At temperatures less than 31.3° C.,the CO₂ exists as a subcritical liquid. Above this temperature, it is asupercritical fluid. The amounts of CO₂ employed were in excess of thesolubility limit for CO₂ in the suspensions. Thus, the mixtures sprayedcontained two liquid phases. A Graco 431 (0.79 mm) orifice was utilizedfor this series of tests. Spray times from 2 to 11 minutes were run.Results are shown in Table 5 below.

                  TABLE 5                                                         ______________________________________                                                        Slurry   CO.sub.2 flow                                                                        Lbs CO.sub.2                                                                         ON/OFF                                 Pressure                                                                              Temp    flow rate                                                                              rate   per lb.                                                                              cycle                                  (bar)   (°C.)                                                                          (kg/hr)  (kg/hr)                                                                              slurry time                                   ______________________________________                                        70.0    18      8.0      4.3    .534    .15/2.0                               87.2-90.7                                                                             21      7.8      2.2    .285    .125/2.25                             83.8-94.1                                                                             23      6.6      2.6    .396    .125/2.25                             87.2    23      7.4      2.5    .34     .125/2.25                             87.2-101.0                                                                            21      7.6      4.0    .524    .125/2.25                             56.2    21      7.8       0.9*  .119   .125/2.0                               56.2-57.9                                                                             20      7.4      2.6    .359   .125/2.0                               52.7-59.6                                                                             21      6.9      2.4    .353   .125/2.0                               47.9-57.9                                                                             22      6.8      1.6    .240   .125/2.0                               56.2-57.9                                                                             21      8.6      2.2    .256   .125/2.0                               54.8-56.2                                                                             21      7.6      2.5    .324   .125/2.0                               76.9-80.3                                                                             33      7.4      4.2    .567   .125/2.0                                *plugged                                                                 

EXAMPLE 13 Particle Coating/Extrusion Trials

The batch spray apparatus of FIG. 1 was set up to allow spraying into a3 cubic foot (0.085 cubic meter) ribbon blender. An amount of 74 pounds(33.6 kilograms) of polypropylene powder was placed into the ribbonblender. An additive slurry mixture containing 25% Stabilizer 2, 25%Stabilizer 3, and 50% Carrier Liquid 1 was placed into the autoclave.Spray conditions of 1060 psig (74.1 bar) and 50° C. were maintained. TheON/OFF cycle timers controlling the opening and closing of the spray gunwere adjusted to 0.1 sec. ON and 4.95 sec OFF, to deliver an averageflow rate of 3.8 lb/hr (1.725 kilograms/hr.) to the blender. Targetlevels of 800 ppm Stabilizer 2, 800 ppm Stabilizer 3, and 1600 ppmCarrier Liquid 1 were chosen to be delivered to the resin in the ribbonblender. The spray nozzle was located 8.5 inches (21.6 cm.) above theresin level in the ribbon blender, and was directed to spray near thecenter of the blender. The ribbon blender rotated at 60 RPM during the208 sec spray time, and the rotation continued for another 10 minutesbefore being stopped. The blender contents were then discharged into afiber drum. During discharge, four one gallon (3.8 liter) samples weretaken and saved. The resin remained free flowing throughout the test andduring discharge from the blender.

Another test was carried out by dry blending Stabilizer 2 and Stabilizer3 with polypropylene powder. Target levels of 800 ppm Stabilizer 2 and800 ppm Stabilizer 3 were chosen. A total of 68 pounds (30.9 kg) ofpolypropylene was charged to the ribbon blender. An additive blendcontaining 24.7 g Stabilizer 2, 24.7 g. Stabilizer 3, and 597 g ofpolypropylene (obtained from the 68 lb (30.9 kg) charge) was mixed welland continuously fed into the center of the operating blender over a 210second time. The blender was again agitated for 10 minutes after theaddition was complete.

Resin bulk density and particle size distribution were measured for thedry mixed and sprayed additive mixtures discharged from the ribbonblender. A particle size distribution, as measured by dry screening, issummarized below in Table 6:

                  TABLE 6                                                         ______________________________________                                        Dry Blended Polypropylene Powder                                                                               Cumulative                                                                    % Smaller                                    Particle  Weight of    Percent of                                                                              Than                                         Size      Sample       Sample    Particle                                     (Microns) Retained, gm Retained  Size                                         ______________________________________                                        3360      10           2.32      97.68                                        2380      14           3.24      94.44                                        2000      14           3.24      91.19                                        1680      30           6.95      84.24                                        1190      60           13.90     70.34                                        707       137          31.75     38.59                                        595       29           6.72      31.87                                        297        103.5       23.99      7.88                                        210       17           3.94       3.94                                        177        8           1.84       2.09                                        149        4           0.93       1.16                                        <149       5           1.16      --                                           Spray Blended Polypropylene Powder                                            3360      10           2.38      97.62                                        2380      14           3.33      94.29                                        2000      14           3.33      90.95                                        1680      23           5.48      85.48                                        1190      66           15.71     69.76                                        707       140          33.33     36.43                                        595       33           7.86      28.57                                        297        105.5       25.12      3.45                                        210        4           0.95      2.5                                          177         4.5        1.07       1.43                                        149        3           0.71       0.71                                        <149       3           0.71      --                                           ______________________________________                                    

The bulk density of the additive free resin feed was 18.9 lb/cu.ft.(0.30 g/cc), whereas the bulk density of the spray mixed material was22.2 lb/cu.ft. (0.36 g/cc), and the bulk density of the dry blendedmaterial was 20.2 lb/cu.ft. (0.32 g/cc). A product with a higher bulkdensity and less fine powder was observed for the sprayed additive test.

Next, a one gallon (3.8 liter) sample was compounded in a 3/4 inch (1.9centimeter) Braybender extruder. The sample was extruded at 230° C. Someextruded material was chopped into pellets and some was retained as 1/8inch diameter "rope".

Uniformity of additive distribution was determined on a pellet to pelletbasis using differential scanning calorimetry to measure oxidationinduction time (DSC/OIT). The oxidation induction times for 20 pelletsfrom each sample were determined. The averages and standard deviationsare given below in Table 7:

                  TABLE 7                                                         ______________________________________                                        DSC/OIT Data                                                                                  Mean OIT  Std. Dev.                                           Additive Delivery                                                                             (min)     (min)                                               ______________________________________                                        Dry Additive    44.9      28.1                                                Blending                                                                      Sprayed Additive                                                                              30.0       7.8                                                Blending                                                                      ______________________________________                                    

It is clear that spraying affords much more uniform levels of additionon the resin than dry blending.

Other embodiments of the invention will be apparent to the skilled inthe art from a consideration of this specification or practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope and spiritof the invention being indicated by the following claims.

We claim:
 1. A process for applying a polymer additive material to apolymeric substrate, comprising the following steps:A) forming in aclosed pressurized system a mixture comprising: 1) at least one polymeradditive material which is a solid under standard conditions oftemperature and pressure; 2) at least one liquid carrier materialcapable of dissolving, suspending, or dispersing said polymer additivematerial; 3) at least one viscosity reducing material which is:i) aliquid under the pressure of said closed pressurized system, ii) atleast partially soluble in said liquid carrier material, iii) present insaid mixture in an amount which is effective to cause said mixture tohave a viscosity which renders it sprayable, and iv) volatile understandard conditions of temperature and pressure, and B) spraying saidmixture onto a polymeric substrate.
 2. The process of claim 1 whereinsaid polymer additive material is selected from the group consisting ofantioxidants, neutralizers, metal deactivators, slip agents, lightstabilizers, antiblocking agents, colorants, lubricants, flameretardants, coupling agents, processing aids, antistatic agents,nucleating agents, and blowing agents.
 3. The process of claim 2 whereinsaid liquid carrier material is selected from the group consisting oforganomodified polydimethylsiloxanes, polyalkylene glycols, andpolyethylene glycols.
 4. The process of claim 1 wherein said viscosityreducing material is selected from the group consisting of supercriticalfluids and subcritical compressed fluids.
 5. The process of claim 4wherein said viscosity reducing material is selected from the groupconsisting of carbon dioxide, ammonia, nitrous oxide, xenon, krypton,chlorotrifluoromethane, monofluoromethane, methane, ethane, ethylene,propane, and pentane.
 6. The process of claim 5 wherein said viscosityreducing material is selected from the group consisting of carbondioxide and nitrous oxide.
 7. The process of claim 1 wherein in thespraying step said polymer additive material is reduced in particle sizerelative to its initial particle size.